I have an account in LinkedIn since 2 years !! it can help in many things !! For example personally my boss contacted me for a job from LinkedIn
We are active on LinkedIn. There's a great opportunity to connect with professionals around the world. Not to mention there's plenty of job offers and opportunities. Although the groups and comment idea is a little too consuming. You get an email for every single comment and posting. There are settings to disable these, but still when you go online it not easy to find them without the link. LinkedIn could do better. As a professional network idea is great. But it needs a bit of work.